1. Field of the Invention
The invention relates to an apparatus for imparting a controlled relative displacement of two parallel surfaces along a single axis or along two orthogonal axes. The apparatus uses a force-generating means and connecting beams acting in concert to produce a relative displacement of two rigid parallel frames. An imaging means is mounted on one rigid frame and a photosensitive matrix on the other to provide an electro-optical detector system in which the image field may be periodically displaced along a closed trajectory to cover the interstices between the detector elements of the photosensitive matrix. The invention also relates to a method for the use of the apparatus to generate electronic picture information.
2. Information Disclosure
Electronic imaging systems employing solid state image sensors or charge coupled device (CCD) arrays are used to produce standard video resolution (512.times.512 pixel) as well as higher resolution images. Image sensors are utilized in television cameras and other electro-optic systems to convert a visual presentation on the sensor's surface into a serial pulse train of electrical signals. The pulse train is then processed and conditioned for whatever purpose is to be made of information contained therein. When the CCD is used for image reproduction as part of an electro-optical depiction system it is placed in the focal plane of an optic system comprised of lenses, colimators, etc. Multiplexers associated with the component CCD's convert the image sensed in a focal plane to a train of pulses, the amplitude of which is directly proportional to the intensity of illumination occurring at each photo site or pixel of the sensors.
Silver halide photographic images can be captured with an acceptable loss in resolution if an array with at least 2000.times.3000 pixels is used. A 4000.times.6000 pixel array is probably closer to optimum. At present, the largest arrays contain about four million pixels in a 2000.times.2000 array. At this density the arrays are very expensive and still do not produce images with silver halide photographic resolution. If the number of pixels is simply increased in a CCD to satisfy the need for high integration, the chip size is increased. If the number of pixels is increased and their size decreased in order to increase the number of pixels without changing the chip size, the integration of pixels must be greatly enhanced. In this case it is technically difficult to prepare the high density CCD and even if fabrication techniques allow the manufacture of such a CCD, the circuit configuration becomes complicated and the power consumption becomes high, giving rise to new problems.
In order to address the problem of the number of pixels versus packing density, the CCD may be periodically displaced (dithered) relative to incident image light thereby allowing each pixel to capture information on several adjacent segments of the image. In this fashion a low resolution array can be used to produce high resolution images. The CCD is configured as a sparse array and the image is scanned over the array as disclosed, for example in U.S. Pat. No. 4,633,317 (Uwira et al.). An example of a sparse array is shown in FIG. 1 discussed below. The small dark squares represent the pixel active area and the remaining space is inactive. The value G is the ratio of the active width to the pixel pitch and need not be the same on both axes. If G is 0.5 on both axes, then a 1000.times.1500 array can be used to produce the same resolution as a 2000.times.3000 array. To capture an image, the image and array have to be moved relative to each other so that each quadrant of the area defined by the horizontal and vertical pixel pitch fall on the active quadrant as shown in the bottom right pixel in FIG. 1. The art discloses methods for moving an image relative to a CCD array.
U.S. Pat. No. 4,517,603 (Epsztein and Guyot) discloses a device for producing televised pictures with a high degree of resolution. The device comprises a photosensitive matrix which receives an optical image and an electromechanical apparatus for displacing the matrix with respect to the image. The displacement is equal to half the size of the pixel. In the construction of the device, the photosensitive matrix is surrounded by a mechanical support guided by members which also act as end of travel stops for limiting the total displacement of the matrix to a half line. The support is subject to a restoring force supplied by springs whose rigidity must be such that the matrix displacement takes place in less than about 2 microseconds. The support is subject to an exciting force supplied by a moving coil immersed in a radial magnetic field and controlled by a square signal generator.
U.S. Pat. No. 4,554,586 (Tanuma et al.) discloses a solid state image sensing device which includes a base board fitted with a CCD serving as an area sensor and a pair of bimorph piezoelectric vibrating elements which jointly vibrate the CCD relative to an incoming image in a plane substantially parallel with the surface of the base board. The piezoelectric vibrating elements are elastically held above the base board by supporting plates having a spring action.
U.S. Pat. No. 4,581,649 (Morokawa) discloses an pickup system which has an image sensor including a plurality of photodetectors arranged in two dimensions and an optical system having a lens for forming an image on the image sensor. A vibrator is provided for vibrating the image on the image sensor so as to oscillate the picture data and a scanner is provided to be operative in synchrony with the vibration of the image to change the oscillated picture data to data for a fixed image. The vibrator comprises a pair of piezoelectric vibrator elements disposed on both sides of the support plate which is supported on a support. A counterbalance is secured to an electrode of the vibrator element so that when both vibrator elements are driven by a signal from a driving signal source, the image sensor and balance are reciprocated and the vibration of the system is canceled.
U.S. Pat. No. 4,607,287 (Endo et al.) discloses a solid-state image sensing device in which a CCD is coupled to fixed bimorph piezoelectric vibrators by which it is given a wobbling-swing drive during image pickup. This wobbling-swing drive is controlled by a controller which provides two vibrations: a swing vibration and a wobble vibration superimposed on the swing vibration so that the pickup operation is performed at each sampling position while wobbling when each pixel is positioned in each field.
U.S. Pat. No. 4,633,317 (Uwira et al.) discloses a high resolution electro-optical detector system incorporating a mosaic CCD. The image of the field is periodically displaced along a closed trajectory cover the interstices between the detector elements of the mosaic detector. The image is moved relative to a stationary mosaic detector. Each image element performs a movement clockwise along a closed circular trajectory. The image is rotated by means of a plane mirror which is supported on three piezoelements. The mirror carries out a uniform rotating motion when three alternating voltages mutually displaced in phase by 120.degree. are supplied to the three piezoelements which are angularly spaced by 120.degree..
U.S. Pat. No. 4,652,928 (Endo et al.) discloses a solid state image sensing system which includes a CCD and a vibration table. The vibration table moves the CCD in such a manner that it is vibrated in a horizontal direction in one vibration cycle consisting of two succeeding frame periods each having two fields. The CCD is fixed to the rear side of a vibration table opposite its image pickup side which faces a lens. The table comprises a bimorph piezoelectric element and vibrates in a cycle of two frame periods under a predetermined complicated vibration mode in response to a swing drive signal.
U.S. Pat. No. 4,755,876 (Dangler) discloses an image scanner which utilizes a dither plate to steer an image onto a sparsely-populated image sensor. A DC motor, which is responsive to a servo control is used to position the dither plate relative to the sensor. The position of the dither plate is sensed by a linear proximity sensor which is part of a closed-loop servo control for the motor.
U.S. Pat. No. 4,947,239 (Kondou and Ono) discloses a swing-driven solid state imaging device which has a CCD image sensor, a stacking piezoelectric element and a package structure. The piezoelectric element serves as an actuator for vibrating the image sensor in a plane substantially perpendicular to the image.
In the devices of the art (Tanuma, Morokawa, Endo, Iwira, Endo II and Kondou) piezoelectric actuators (PZT) are used to scan a CCD array through one pixel pitch so that a sparse array can be used to capture an image. Drift, which leads to unreliable positioning of the array, is one of the drawbacks of PZT's and PZT power supplies tend to be complicated. Moreover piezoelectric drive elements are expensive and are therefore not commercially suitable in situations where expense is a critical factor. Magnetic displacement of the CCD platform (Epsztein) using a platform with a small spring constant leads to overshoot and oscillation after displacement. A wedged rotating plate with servo motor control (Dangler) has also been used but this technique is expensive to implement.
There is thus a need for a robust mechanical system that is both precise and inexpensive.